1. Field of the Invention
This invention relates to a coordinate measuring instrument wherein a shape and the like of a workpiece to be measured are measured from displacements of a measuring element made displaceable, with respect to the workpiece rested on a bedplate, in directions of axes of X, Y and Z perpendicularly intersecting one another.
2. Description of the Prior Art
Heretofore, there has been known a coordinate measuring instrument wherein a measuring element is brought into abutting contact with the surface of a workpiece and a shape and the like of the workpiece are measured from displacements of the measuring element. The measuring instrument of the type described is capable of measuring the workpiece with high accuracies, and hence, is utilized in all fields of industries.
FIGS. 1 and 2 show the appearances of the coordinate measuring instruments which have been commonly used and are different in type from each other. Referring to FIG. 1, a supporting structure 1 comprises a base 2 and a surface plate 3 as being a bedplate disposed on this base 2, and a gate-shaped measuring element support member 4 is supported on this surface plate 3 through bearings 5 and 6 in a manner to be movable in a direction of the Y axis (longitidinal direction). Provided between the surface plate 3 and the measuring element support member 4 is a Y axis direction displacement detector 7 consisting of an optical displacement detector and the like, which can automatically detect a displacement of the support member 4 in the direction of a Y axis.
The measuring element support member 4 includes a transverse member 8, and a slider 9 is supported on this transverse member 8 in a manner to be movable in a direction of an X axis (lateral direction). Provided between this slider 9 and the transverse member 8 is an X axis direction displacement detector 10 consisting of an optical displacement detector and the like, which can automatically detect a displacement of the slider 9 in the direction of the X axis. The slider 9 is provided with a prismatic spindle 11 in a manner to be movable in a direction of a Z axis (vertical direction), and a measuring element 12 is provided at the bottom end of this spindle 11. Further, provided between this spindle 11 and the slider 9 is a Z axis direction displacement detector 13 consisting of an optical displacement detector and the like, which can automatically detect a displacement of the spindle 11 in a direction of a Z axis.
In the coordinate measuring instrument shown in FIG. 2, a supporting structure 1 comprises a base 2, a surface plate 3 disposed on the base 2 and supports 14, 15 erected from opposite sides of the upper surface of this surface plate 3. A measuring element support member 4 consisting of a transverse member 8 is provided on these supports 14 and 15 in a manner to be movable in the direction of the Y axis through air bearings 5 and 6, and other respects of construction are identical with those of the construction of the coordinate measuring instrument shown in FIG. 1.
Being seized with the idea that rugged construction having no portions to be adjusted can secure high accuracies, in the conventional coordinate measuring instrument of the type described the positional reference of construction of the measuring instrument is sought on the upper surface of the surface plate 3, the support portions of the measuring element support member 4 or the supports 14 and 15 are precisely uprightly erected on this surface plate 3, a transverse member 8 is precisely horizontally racked across these support portions or the supports 14 and 15, a movable slider 9 is provided on this transverse member 8 in such a manner that a spindle 11 supported by this slider 9 can be disposed precisely vertically and so forth. Thus, the conventional coordinate measuring instrument has been constructed such that, the various portions are successively built up while being adjusted on the basis of the surface plate 3. Furthermore, the support portions or the supports 14 and 15 of the measuring instrument support member 4 should bear the weights of the transverse member 8, the slider 9 and so forth, and hence, the shapes of the leg portions should necessarily be rendered large-sized.
For this reason, in the conventional construction the portion occupied by the leg portions is large, and hence, the effective area usable for the measuring is reduced, and the effective height is limited by the heights of the supports. With the construction shown in FIG. 2, linear movement of the workpiece to be measured to and from the upper surface of the surface plate 3 is performed with difficulties to a considerable extent owing to the presence of the fixed supports 14 and 15, and a workpiece larger than the span across the supports cannot be mounted on the surface plate 3. Thus, such a disadvantage has been presented that the scope of measuring capacity is very small for the large size of the measuring instrument.
Furthermore, with the method of successively building up the various portions after they are adjusted, when it is found that the accuracy is low after the final assembling, it is not known what portion is to be adjusted. Thus, such a disadvantage has been presented that all of the adjustments and assemblings should be repeated from the beginning. In consequence, in the conventional construction, the accuracy of finishing of one of the parts affects the overall accuracy to a great extent, and any deviation in adjustment or the like in the initial stage cannot be corrected or improved, thus resulting in doing all the adjustment and assembling by lapping over from the beginning. Since the overall accuracy depends upon the skill level of the operators in assembling to a considerable extent, the high skill level in working is required from the operators, and moreover, since parts finished with high accuracy must be used, the cost of manufacture is increased to a considerable extent. Further, since such a method is adopted that the various portions are successively built up, it becomes difficult to assemble the products at the site, which leads to inconvenient transportation of the products and so forth, thus resulting in cumbersome handling of the conventional coordinate measuring instrument.
Since the conventional coordinate measuring instrument is of such an arrangement that displacements of the measuring element are to be measured as referenced from the upper surface of the bedplate, it is necessary to move the measuring element support member supporting the measuring element in parallel to the upper surface of the bedplate.
In view of the above, heretofore, guide rails finished with high accuracy have been directly affixed to the upper surface of the bedplate in parallel to each other by means of fittings for exclusive use with bolts. In consequence, there have been presented such disadvantages that a great amount of labor is needed for the installation of the guide rails, out of the area of the upper surface of the bedplate the effective portion put to use for resting a workpiece to be measured is small, and a workpiece of heavy weight cannot be parallelly moved from one side of the bedplate to be rested thereon.
On the other hand, there are some cases where, for example, the guide rails are suspended from the ceiling of a house, or the guide rails are disposed on the ground through a bed in no connection with the bedplate. In this case, a great amount of labor is needed for obtaining parallelism between the upper surface of the bedplate and these guide rails, and moreover, anti-vibration measures for the guide rails must be taken, thus resulting in increased costs and lowered accuracy.
Further, in the conventional coordinate measuring instrument, a stopper is provided between the guide rails and the measuring element support member to prevent the measuring element support member from falling off the guide rails.
However, since the stopper is affixed to the guide rails or the like, when the measuring element support member abuts against the stopper and is stopped thereat, the measuring element support member is deflected, deformed and so forth, thus resulting in lowered measuring accuracy.
Now, in the measuring instrument of the type described wherein an accuracy as high as in .mu.m order is required, it is an essential requirement to prevent the structure of the measuring instrument support member and the like from being deformed. Heretofore, it has been admitted that there is little possibility that the measuring instrument support member abuts against the stopper disposed at the outer-most position in the scope of measuring capacity to thereby be deformed and so forth. Consequently, the above-described design has been adopted.
However, practical operations are concentratedly based on the relations between the workpiece to be measured and the measuring element, and hence, the measuring element support member often reaches the limited portion of the scope of movement. Moreover, the portions of the measuring element support member are very smoothly movable, and hence, often abut against the stopper. In consequence, there has been presented the disadvantage that the measuring element support member is progressively deformed, resulting in lowered measuring accuracy.
Furthermore, in the conventional coordinate measuring instrument, there are used measuring elements having various forward ends different from one another in accordance with the purposes of use. In the mounting constructions, in each of which one of the measuring elements of the type described is mounted to a spindle having a mounting portion for the measuring element of the type described, the shapes of shank portions of all the measuring elements are made identical with one another in measuring instruments of a given type, and round holes meeting the shapes of the shank portions are penetratingly provided in the mounting portions of the measuring elements of the spindles, and engagements therebetween are effected.
Therefore, heretofore, it has been necessary to prepare various measuring elements having forward ends different from one another for different measuring instruments, thus resulting in an extreme inconvenience in use.
As described above, normally, the shapes of the shank portions of the measuring elements in the measuring instruments of the same type are made identical with each other, however, there are cases where the identical shapes cannot be adopted depending upon the purposes of use. More specifically, in performing marking-off works by use of the measuring element, an appreciable value of load acts on the measuring element unlike an ordinary contact, and so it is preferable to make the shank portion larger in diameter than an ordinary one. Further, this is true of the case where a measuring element by far longer than an ordinary one is used.
However, heretofore, in order to make the shank larger than an ordinary one, it has been necessary to change the shape of the spindle. However, the fact is that the operators have been using the conventional measuring elements as they are, enduring inconvenience.
Further, in the conventional measuring instrument of the type described, there has been known a so-called universal probe (measuring element) in which the forward end portion is made tiltable with respect to the main body portion thereof. This measuring element is secured to a Z axis spindle through its shank portion integrally formed on the main body portion thereof, and the forward end portion thereof is tiltable with respect to the axial direction of the spindle.
However, the conventional measuring element can be brought into contact with the inner wall of a hole formed in an inclined surface, and the spindle itself is not tilted, but moved only in the direction of the Z axis, i.e., the vertical direction, and hence, processing of the measured value in accordance with the contact of the measuring element should be strictly performed three-dimentionally, thus requiring calculations.
Therefore, necessity has been voiced for a coordinate measuring instrument wherein a depth of a hole formed in an inclined surface and the like are processed one-dimentionally without requiring calculations.
Furthermore, in the conventional measuring instrument of the type described, from the necessity for performing measurement in a condition where the workpiece to be measured and the measuring element are moved relative to each other, there are provided various guide rails and an engageable block movable along these guide rails. In this case, in the measuring instrument for performing precision measurement and requiring a high speed measurement such as a coordinate measuring instrument, there has been developed a device wherein the guide rails and the engageable block are finely fed during precision measurment and freely, manually transferred, releasing this fine feed during high speed movement.
Heretofore, the fine feed device of the type described, as disclosed in Japanese Patent Kokai(Laid-Open) No. 10759/74, comprises a feed screw, a half nut openably, threadably coupled to this feed screw and an arm holding this half nut and opening or closing the half nut, and, free feed and fine feed can be performed in accordance with the opening or closing operation of this arm.
However, the conventional device as described above presents such disadvantages that the construction is complicated and expensive, and, when the half nut is mistakenly closed during free feed, the main parts such as the feed screw and the like are damaged.